Interpretive Summary: Many streams in agricultural watersheds are characterized by unstable channel boundaries. Erosion in these unstable channels destroys valuable agricultural land, and also degrades the stream habitat for fish and other aquatic organisms. Determining the velocity and area of the flows in a stream that are responsible for maintaining the channel and the aquatic habitat are essential information for use by river engineers to restore impacted channels to a more natural state. The flows which move the most sediment and are necessary to maintain the channel were calculated for three sites on the Goodwin Creek Experimental Watershed. It was found at two of these sites that a range of flows was necessary to maintain these channels because of the large range of sediment sizes present on the channel boundaries. This information is valuable for watershed managers and researchers for guidance in managing impacted streams in similar agricultural watersheds and channels in which flow and sediment movement data are not available.

Technical Abstract:
Dominant discharge was evaluated for three sites on the incised Goodwin Creek Experimental Watershed. The channels at the three locations (stations 2, 5, and 13) drain 17.9, 4.2, and 1.2 square kilometers, respectively. Measured flow and total sediment load relations derived from three types of sediment samples at the three sites allowed the effective discharge to be calculated at the three sites. Effective discharges were found to occur at recurrence intervals of approximately one year, and all were considerably less than bankfull. Dominant discharge for streams with a wide range of channel boundary sediment sizes is best represented by a range of flows rather than one single flow. The effective discharges for one site were found to correspond to about three times the critical shear stress for the bed material.